1. Technical Field
The present disclosure relates to the field of digital image processing, and more particularly to the processing applied to digital images of the eye in identification or authentication applications.
2. Description of the Related Art
Iris recognition is a tried and tested biometric identification technique, provided that the image to which the analysis and identification processing is applied is an exploitable image. In particular, the performance of the recognition algorithms greatly depends on the sharpness of the image of the iris to be identified. Now, in most applications, and particularly in so-called “embedded” applications (for example, for access control to a mobile telephone or laptop computer, for a hardware key, etc.), the camera (digital sensor and lens) used has no auto-focus device, adjusting the (actual or simulated) focal length according to the distance.
Moreover, to obtain a sufficient resolution of the iris, the images are taken at a relatively short distance, generally in the order of 10 to 30 cm. The result is a low depth of field (range of distance between the camera and the eye, in which the image is sharp). Added to the fact that the eye is spherical, this low depth of field can cause differences in sharpness between zones of a same image of the eye. The user must be very cooperative by positioning himself in a relatively reduced sharpness zone. In practice, the user moves to position himself at a sharpness distance.
Processing is therefore often done prior to the actual iris recognition to select a sufficiently sharp image. This prior processing involves selecting out of a certain number of images, one or more sharp images which are subjected to an iris recognition algorithm.
The present disclosure relates more particularly to the selection processing applied to images of a same eye to select sufficiently sharp images to be sent to the recognition device.